The present invention relates to the use of cables in certain construction techniques and more specifically to the methods used to attach load-transmitting elements to a structural cable.
An important, though not exclusive, application of the invention is that of suspension bridges. In this application, hangers transmitting the load of the deck have to be attached to a bearing cable of the bridge, formed of one or more bundles of strands.
This attachment is generally performed by means of collars, each being made up of several shells which are clamped around the cable using means such as bolts, each hanger being fixed to one of the shells of its collar. The clamping force applied to the collar enables the bearing cable to absorb, by friction, the tangential components of the forces transmitted by the hangers.
French patent 2 739 113 proposes a bearing cable made from a bundle of "coherent" strands. Each coherent strand comprises a strand strictly speaking, made up of a stranded assembly of seven or more metal wires, coated with an adherent elastomer material and surrounded by an individual sheath of plastic material, whereby the strand and the elastomer material fill the interior space of the individual sheath.
This strand structure limits the force needed for the clamping action, which improves the reliability of the system.
European patent application 0 789 110 discloses the insertion of filler elements in a cable made up of individually protected strands (for example coherent strands), the filler elements being placed at the level of the attachment collars so that they fill the interstices between the individual sheaths of the assembled strands, the cross-section of said interstices being triangular in shape with curved sides.
This arrangement ensures that the clamping forces of the collars are transmitted more evenly to the strands under tension. At the level of the collars, the bearing cable is contained in a tubular envelope made of plastic material and deformable elements are inserted between the envelope and the bundle of strands. This assembly is crushed instantly when the collars are clamped and is also subjected to a delayed crushing action due to the creep of the materials, generally plastic, from which the envelope, the deformable elements and/or the filler elements are made.
In the typical example of a collar having an internal diameter of 400 mm, the delayed settling of this assembly under the effect of creep is typically in the order of 1 mm. This value may cause the collar to loosen, which could have disastrous consequences. As a result, regular maintenance work has to be carried out to check the tightness of the clamped collars and re-clamp them as required.
An object of the present invention is to improve the clamping action of the attachment collars on a structural cable.